1. Field of the Invention
The present invention relates to a high-thrust linear motor in which armature coils and field magnets are arranged linearly to convert electrical energy supplied by the armature coils directly into linear kinetic energy with high thrust through the field magnets.
2. Discussion of Related Art
There is a linear motor that converts electrical energy directly into linear kinetic energy by utilizing repulsive or attractive magnetic force. This linear motor, for example, has a moving part consisting essentially of an armature winding formed from wound coils (electromagnets) and a stationary part having field magnets (permanent magnets) arranged along a guide. The moving part is caused to travel linearly along the guide serving as a stationary-side member by utilizing repulsive or attractive magnetic forces acting between the armature coils and the field magnets, thereby converting electrical energy into linear kinetic energy.
Linear motors arranged as stated above include two different types, i.e. coreless linear motors having no core in the armature winding, and cored linear motors having a core in the armature winding.
The coreless armature winding consists only of wound coils and therefore causes minimal variations in travel (cogging) of the moving part due to variations in magnetic reluctance that occur during the travel of the moving part. Further, the coreless armature winding is light in weight because it has no core. Therefore, the coreless armature winding is generally used in small-sized linear motors.
The cored armature winding can be arranged to provide thrust 2 to 3 times as high as that of coreless linear motors simply by inserting a core (magnetic member) into the hollow portion of an air-core armature winding, which has no core. Therefore, the cored armature winding is usually used in high-thrust linear motors.
There is a linear motor in which a large number of coils are wound in a plurality of slots formed in a core to form an armature winding, and the effective conductor portions of the armature coils are opposed to field magnets. It is known that this type of linear motor provides increased thrust because an increased number of coils can be wound in the slots.
In other words, it is known that high thrust can be obtained with a linear motor by adopting an arrangement in which: (1) a cored armature is used; (2) slots are formed in the core of the armature; and (3) a large number of coils are wound in the slots.
Next, a conventional cored linear motor having coils wound in slots will be described. FIGS. 1 and 2 are a front view and a longitudinal sectional view, respectively, showing the arrangement of the cored linear motor. This cored linear motor is a three-phase linear motor and has a moving part 1 and a stationary part 2 as shown in FIG. 1.
As shown in FIG. 2, the moving part 1 includes a core 1a and a table 1b secured to the upper surface of the core 1a. The moving part 1 further includes coils C1, C2 and C3. The core 1a is formed with slots S. The coils C1, C2 and C3 are prewound coils and each inserted into two slots S separated by other slots S. The core 1a and the coils C1, C2 and C3 constitute an armature winding.
It should be noted that the reason why the prewound coils C1, C2 and C3 are inserted into the slots S is to facilitate the assembly. The coils C1, C2 and C3 are inserted in the following sequence. First, a U-phase coil C1, a W-phase coil C2 and a V-phase coil C3 are inserted into respective pairs of slots S in the order mentioned so as to lie adjacent to the innermost parts of the slots S. Thereafter, a V-phase coil C3 is inserted into two slots S in such a manner as to be superimposed on the U-phase coil C1 and the W-phase coil C2 so that the V-phase coil C3 is different in electrical angle from the phases inserted into the innermost parts of the slots S. Similarly, a U-phase coil C1 is inserted into two slots S in such a manner as to be superimposed on the W-phase coil C2 and the V-phase coil C3 so that the U-phase coil C1 is different in electrical angle from the phases inserted into the innermost parts of the slots S.
Meanwhile, the stationary part 2 is, as shown in FIGS. 1 and 2, formed from a yoke 2a and field magnets (permanent magnets) 2b. The yoke 2a and the field magnets 2b are disposed to extend linearly so as to face the moving part 1.
When the coils C1, C2 and C3 are energized, electric currents flow in the directions of the arrows in FIG. 3, thus producing magnetic flux. Consequently, repulsive or attractive forces act between the coils C1, C2 and C3 and the field magnets 2b opposed thereto. Thus, thrust is generated in the leftward or rightward direction as viewed in FIGS. 2 and 3, causing the moving part 1 to move.
With the prior art, however, a problem arises when it is intended to achieve a reduction in size of a linear motor with a cored armature winding having the above-described conventional structure. That is, because it is impossible to obtain a large amount of winding of coils in comparison to the weight of the core, the cored armature winding is inferior in the level of attainable thrust to a coreless armature winding having the same weight. This has heretofore been an obstacle to achievement of a compact cored linear motor.
In addition, the conventional cored linear motor having the above-described structure suffers from the problem that the relative movement of the magnetic field is not smooth because of the manner of winding the coils. That is, after a U-phase coil C1 and a W-phase coil C2 have been inserted, a V-phase coil C3 is inserted so as to lie over the area between the U-phase coil C1 and the W-phase coil C2. Therefore, there are overlaps between the coils, and this prevents smooth relative movement of the magnetic field.
On the other hand, when prewound coils C1, C2 and C3 are inserted with a phase (electrical angle) displacement, as shown in FIG. 2, there is a blank space where no coil is wound in a slot S at each end of the core 1a, and the amount of winding of coils on the core 1a is correspondingly reduced. Accordingly, a desired high thrust cannot be obtained.
An object of the present invention is to provide a high-thrust linear motor in which the amount of winding of coils can be increased in comparison to the weight of the core to obtain increased thrust and the linear motion of the moving part is favorably smooth.
Another object of the present invention is to provide a method of producing a high-thrust linear motor that allows coils to be wound in such a manner that there is no blank space where no coil is wound in a slot at each end of the core.
To attain the above-described objects, the present invention provides a high-thrust linear motor including a magnetic member having a plurality of slots formed in series in an axial direction thereof. The slots extend from both sides of the magnetic member in opposite directions intersecting the axial direction in corresponding relation to each other. Coils are wound in respective pairs of slots on both sides of the magnetic member. Field magnets extend in the axial direction at both sides of the magnetic member so as to face an effective conductor portion (a portion contributing to the generation of thrust) of each of the coils. Each field magnet has a plurality of pairs of magnetic poles magnetized in the axial direction.
With the above-described arrangement, because the coils can be wound over both sides of the magnetic member through the slots formed on both sides of the magnetic member, the space efficiency (density) of the coils is increased, so that it is possible to obtain higher thrust than in the case of the conventional cored linear motor. Accordingly, it becomes possible to attain a compact cored linear motor.
The high-thrust linear motor according to the present invention has the above-described matters as essential constituent elements. However, the following matters may be added to the constituent elements:
The arrangement may be such that the coils have a plurality of phases and are wound in respective pairs of slots in the magnetic member in such a manner that each pair of adjacent phases are different in electrical angle from each other.
With the above-described arrangement, it is possible to obtain a smooth operating condition equal to that obtained with a distributed winding type coil.
The high-thrust linear motor according to the present invention may further include a cover member for covering the magnetic member and the coils approximately entirely, exclusive of effective conductor portions of the magnetic member and the coils.
With the above-described arrangement, the cover member covers the armature having the coils wound on approximately the entire area of the magnetic member, and this cover member is secured to a table or other moving member, whereby the armature is prevented from directly contacting the table or other moving member, and the armature can be surely secured to the table or the like through the cover member.
Further, the arrangement may be such that the cover member is divided into a pair of cover elements disposed to cover the magnetic member and the coils approximately entirely, and connecting members for integrally connecting together the pair of cover elements are provided.
The above-described arrangement facilitates the operation of securing the magnetic member and the coils to the cover member.
Furthermore, the connecting members may be formed from a material having high thermal conductivity and disposed in contact with or close proximity to the magnetic member.
With the above-described arrangement, the connecting members act as a radiator, whereby heat generated from the coils can be dissipated to the outside without storing it in the magnetic member. Accordingly, it is possible to prevent reduction of thrust as occurs when the magnetic member is heated. It should be noted that a metal, for example, aluminum, is preferably used as a material having high thermal conductivity.
Furthermore, a non-magnetic material may be filled in the space between the magnetic member and the coils on the one hand and the cover member on the other.
With the above-described arrangement, the magnetic member, the coils and the cover member are integrated in close contact with each other. Therefore, none of the magnetic member, the coils and the cover member will be deformed when the assembly of these members moves linearly or stops. Accordingly, the assembly of the magnetic member, the coils and the cover member is suitable for use as a moving part.
In addition, the present invention provides a method of producing a high-thrust linear motor. According to the high-thrust linear motor producing method, a magnetic member is prepared which has a plurality of slots formed in series in an axial direction thereof. The slots extend from both sides of the magnetic member in opposite directions intersecting the axial direction in corresponding relation to each other. Then, coils are wound in respective pairs of slots on both sides of the magnetic member while the magnetic member is being rotated.
According to the method of the present invention, the coils are wound directly in the slots unlike the conventional process in which prewound coils are inserted into slots. Therefore, there will be no blank space where no coil is wound in the slots. Accordingly, it is possible to obtain a smooth operating condition equal to that obtained with a distributed winding type coil. Thus, it is possible to produce a high-thrust linear motor having increased space efficiency and capable of providing increased thrust.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.